Stereotactic body radiation therapy (SBRT) for prostate-specific membrane antigen positron emission tomography (PSMA-PET)–detected oligometastatic prostate cancer: A real world analysis of patients treated in a reference center.

Abstract

e17156 Background: Stereotactic body radiation therapy (SBRT) is a useful therapy for patients with oligometastatic prostate cancer (OPC). SBRT benefits patients by delaying androgen deprivation therapy (ADT) and thus avoiding its side effects and preserving quality of life. The aim of this study is to investigate real-world outcomes of applying SBRT to patients with OPC, who were pre-selected by PSMA-PET and did not receive concomitant ADT. Methods: A retrospective analysis of medical records was conducted at a reference oncology center in Brazil with the primary objective of evaluating androgen deprivation therapy free-survival (ADTFS). Secondary objectives included the assessment of radiologic progression free survival (PFS), PSA response, local control rate (LCR) and treatment related toxicity. All patients were oligometastatic by PSMA-PET (up to 5 lesions) and underwent SBRT without concomitant ADT. Patients were excluded if they received ADT with SBRT or started ADT within 30 days of completing SBRT. Toxicity was measured according to the Radiation Therapy Oncology Group (RTOG) score system. Results: Between 2017 and 2024, 86 prostate cancer patients received a total of 137 SBRT treatments. 50 patients were excluded due to concomitant ADT, 4 due to unmet inclusion criteria and 4 due to insufficient medical information. Our final analysis included 28 patients, 7 retreated with SBRT once, and 1 patient twice, totalling 37treatments.The average number of fractions and total dose delivered were 3 fractions (3-5) and 34,8 Gy (30-45), respectively. Median age at treatment initiation was 71 years (55-93). The total number of treated lesions was 69, with 62.3% being bone metastasis, 29.0% in lymph nodes, 7.3% lung lesions and one case (or 1.4%) in the penile bulb. SBRT was used in up to 3 metastases in 91.9% of cases, and in 4 or 5 in the remaining 8,1%. Metachronous disease represented 81% of cases, while 19% were considered synchronous disease. The median follow-up time was 27.1 months. Median ADTFS and PFS were 8,9 and 13,3 months, respectively. LCR was 62.1% in 12 months. Regarding PSA response, 21.6% of patients achieved undetectable rates, 40.6% maintained stable values, 35.1% showed PSA progression, and 2.7% lacked PSA information. RTOG grade 3 toxicity was observed in 5.4% of cases. Conclusions: SBRT is an effective and low toxicity therapeutic option for PSMA-PET selected OPC patients, who are then able to delay ADT.